Dr. Terace Fletcher tfletcher@ptcc.edu CHM1033 Acid-Base Dr. Terace Fletcher tfletcher@ptcc.edu

General, Organic, and Biological Chemistry Acids Arrhenius acids produce H+ ions in water HCl(g) H+(aq) + Cl(aq) are electrolytes have a sour taste turn litmus red neutralize bases General, Organic, and Biological Chemistry

Names of Acids Acids with H + nonmetal prefix hydro- and end with -ic acid. HCl hydrochloric acid Acids with H + polyatomic ion  the end of the name of the polyatomic ion from -ate to -ic acid or -ite to -ous acid. ClO3− chlorate HClO3 chloric acid ClO2− chlorite HClO2 chlorous acid ClO− hypchlorite HClO Hypochlorous acid General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

General, Organic, and Biological Chemistry Bases Arrhenius bases produce OH− ions in water taste bitter or chalky are electrolytes feel soapy and slippery neutralize acids General, Organic, and Biological Chemistry

Some Common Bases Bases with OH ions are named as the hydroxide of the metal in the formula. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH)2 barium hydroxide Al(OH)3 aluminum hydroxide Fe(OH)3 iron (III) hydroxide General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Comparing Acids and Bases General, Organic, and Biological Chemistry

Brønsted–Lowry Acids and Bases According to the Brønsted–Lowry theory, acids donate a proton (H+) bases accept a proton (H+) General, Organic, and Biological Chemistry

NH3, A Brønsted–Lowry Base In the reaction of ammonia and water, NH3 is the base that accepts H+ H2O is the acid that donates H+ General, Organic, and Biological Chemistry

Conjugate Acid–Base Pairs In any acid-base reaction, there are two conjugate acid–base pairs: each related by the loss and gain of H+ one occurs in the forward direction one occurs in the reverse direction conjugate acid–base pair 1 HA + B A− + BH+ conjugate acid–base pair 2 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Conjugate Acid–Base Pairs In the reaction of HF and H2O, one conjugate acid–base pair is HF/F− the other conjugate acid–base pair is H2O/H3O+ each pair is related by a loss and gain of H+ General, Organic, and Biological Chemistry

Conjugate Acid–Base Pairs (continued) In the reaction of NH3 and H2O, one conjugate acid–base pair is NH3/NH4+ the other conjugate acid–base is H2O/OH– each pair is related by a loss and gain of H+ General, Organic, and Biological Chemistry

Strengths of Acids Strong acids (such as hydrochloric acid) completely ionize (100%) in aqueous solutions. HCl(g) + H2O(l) H3O+(aq) + Cl−(aq) Weak acids (such as carbonic acid or acetic acid) dissociate only slightly in water to form a solution of mostly molecules and a few ions. H2CO3(aq) + H2O(l) H3O+(aq) + HCO3−(aq) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Ionization of Water In the ionization of water, H+ is transferred from one H2O molecule to another one water molecule acts as an acid, while another acts as a base H2O + H2O H3O+ + OH− .. .. .. .. H:O: + H:O: H:O:H+ + :O:H− .. .. .. .. H H H water water hydronium hydroxide ion(+) ion(-) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Pure Water is Neutral In pure water, the ionization of water molecules produces small but equal quantities of H3O+ and OH− ions molar concentrations are indicated in brackets as [H3O+] and [OH−] [H3O+] = 1.0 x 10−7 M [OH−] = 1.0 x 10−7 M General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

pH Scale The pH of a solution is used to indicate the acidity of a solution has values that usually range from 0 to 14 is acidic when the values are less than 7 is neutral with a pH of 7 is basic when the values are greater than 7 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

pH of Everyday Substances 16 16

Calculating pH and pOH Mathematically, pH is the negative log of the hydronium ion concentration and pH = −log [H3O+] For a solution with [H3O+] = 1 x 10−4, pH = −log [1 x 10−4 ] pH = [4.0] pH = 4.0 pOH is the negative log of the hydroxide ion pOH = -log[OH-] pH + pOH = 14. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Example of Calculating pH Find the pH of a solution with a [H3O+] of 1.0 x 10−3. STEP 1 Enter the [H3O+] value: Enter 1 x 103 (press 1 EE 3, then change sign) The EE key gives the exponent of 10. STEP 2 Press log key and change the sign: log (1 x 10−3) = [3] STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the coefficient (2): [H3O+] = 1.0 x 10−3 pH is 3.00 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check What is the pH of coffee if the [H3O+] is 1 x 10−5 M? 1) pH = 9.0 2) pH = 7.0 3) pH = 5.0 5.0 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check The [H3O+] of tomato juice is 2 x 10−4 M. What is the pH of the solution? 1) 4.0 2) 3.7 3) 10.3 3.7 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check The [OH−] of a solution is 1.0 x 10−3 M. What is the pH? (hint = figure out pOH first) 1) 3.00 2) 11.00 3) –11.00 11.00 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

[H3O+], [OH-], and pH Values General, Organic, and Biological Chemistry

Testing the pH of Solutions The pH of solutions can be determined using a pH meter pH paper indicators that have specific colors at different pH values General, Organic, and Biological Chemistry

Neutralization Equations In the equations for neutralization, an acid and a base produce a salt and water. acid base salt water HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) H+(aq) + OH−(aq) H2O 2HCl(aq) + Ca(OH)2(aq) CaCl2(aq) + 2H2O(l) H+(aq) + OH−(aq) H2O(l) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

General, Organic, and Biological Chemistry Antacids Antacids are used to neutralize stomach acid (HCl) General, Organic, and Biological Chemistry

Buffers Buffers resist changes in pH from the addition of acid or base in the body absorb H3O+ or OH from foods and cellular processes to maintain pH are important in the proper functioning of cells and blood in blood maintain a pH close to 7.4; a change in the pH of the blood affects the uptake of oxygen and cellular processes General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

General, Organic, and Biological Chemistry Buffers (continued) When an acid or base is added to water, the pH changes drastically to a buffer solution, the pH does not change very much; pH is maintained General, Organic, and Biological Chemistry

Components of a Buffer The components of a buffer solution are acid–base conjugate pairs can be a weak acid and a salt of its conjugate base equal concentrations of the weak acid and the salt of its conjugate base. Should be at reasonably high concentrations to resist changes in H+ or OH- added to the solution. can also be a weak base and a salt of its conjugate acid Acetic acid= weak acid Acetate ion = conjugate base (can buy sodium acetate and mix with acetic acid in water) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Carbonic Acid-Bicarbonate System Buffer system Regulates blood pH pH = 7.35 (vein) pH = 7.4 (artery) Acidosis (pH < 7.35) Alkalosis (pH > 7.45) Exhaling removes CO2 Kidneys secrete or reabsorb H+ and HCO3- Metabolic acids Lactic acid Ketones Phosphoric acids Ammonium Uric acid Carbonic anhydrase CO2 + H2O H2CO3 H+ HCO3-

Summary of Buffer Action Buffer action occurs because the weak acid in a buffer neutralizes base the conjugate base in the buffer neutralizes acid the pH of the solution is maintained General, Organic, and Biological Chemistry